The long-term goal of this research is to develop an objective test of high-frequency hearing to be used in monitoring programs. Such a test is a vital tool that could contribute to the prevention of hearing loss at those frequencies necessary for speech perception and production in children who are exposed to ototoxic agents. It is hypothesized that high-frequency hearing can be tested objectively and is repeatable over time allowing these measurements to be used in ototoxic monitoring programs. This hypothesis is based on evidence demonstrating that high-frequency (>8 kHz) distortion product otoacoustic emissions (DPOAEs), a measure of hair cell functioning in the inner ear, are repeatable in adults. Ototoxicity initially damages high-frequency hearing and typically progresses to lower frequencies. Current monitoring programs utilize behavioral measures, requiring a response to pure tone acoustic stimuli, at high frequencies, as well as conventional frequencies. Additionally, DPOAEs have been used for monitoring hearing at conventional frequencies, requiring no active response from the patient. If behavioral measures cannot be used, existing objective measures will only detect hearing damage once it starts to affect those frequencies that are critical to communication. Ideally, for unresponsive or unreliable (e.g., children) patients hearing would be monitored objectively at high frequencies. Thus, the objective of this research is to determine the repeatability of high-frequency DPOAE measures in children. To attain this objective, linear reflected (spontaneous otoacoustic emissions) and nonlinear distortion emissions (DPOAEs), along with reflectance measures will be measured in older and younger children. Specifically, DPOAE frequency, frequency ratio (group delay), and stimulus level (DPOAE detection thresholds) sweeps, measured alone and in the presence of a suppressor tone to dissociate DPOAE sources, will be completed. Results of the current research will lay the foundation for the development of an objective tool for monitoring high-frequency hearing. Following determination of high frequency DPOAE repeatability in children, patients undergoing ototoxic therapies will need to be monitored to determine the sensitivity of these measures in identifying ototoxicity. DPOAE measures are typically faster than behavioral measures and can target hearing at those frequencies damaged initially by ototoxic agents, preventing damage to hearing at lower frequencies, which are vital to developing communication. The proposed research is innovative because a large database will be established where linear reflected (spontaneous otoacoustic emissions and the fdp place component of the DPOAE, which is essentially a stimulus-frequency otoacoustic emission) and nonlinear distortion (DPOAEs) emissions were measured from 2-16 kHz in older and younger children. The outcomes from this proposed research are the initial steps toward implementation of HF DPOAE testing as a monitoring tool, which will benefit those that are not able to provide reliable behavioral responses to frequencies where hearing is damaged initially by ototoxic therapies. This is expected to positively affect human health, because it will aid in identifying damage to hearing at higher frequencies with the purpose of possibly altering therapies to preserve hearing in the conventional frequencies that are necessary for communication.